This invention generally relates to drill bits, specifically to those with replaceable blade members.
Previous drill bits with replaceable blade members have had poor cutting structure near the center of the drill bit. They have also been attached or affixed to the body of the drill bit but not sufficiently interlocked with the other replaceable blade members.
Most conventional PDC (Polycrystalline Diamond Cutter) or other hardened material fixed cutter drill bits are machined or forged with fixed integral body protruding blades having cutters inserted with a negative or back rake. This allows manufacturers to machine the pockets. The problem presented and which causes the manufacturers to make the drill bits with the negative rake is that the cutter pockets require a small oversize tolerance (e.g. 0.002 inch) for effective brazing and therefore must be machined with a rotating tool which requires a negative rake angle to clear the protruding preceding blade and/or the bottom of the bit. This problem increases as you move towards the center of the bit. This problem is overcome with insertable blades, which can overlap and interlock with each other. The cutter pockets can be machined and cutters placed in the blades prior to the blades being inserted into the body of the bit. This allows the advantage of any cutter rake (i.e. neutral, positive or negative) relative to the bottom of the bit and any cutter angle relative to the bit body center to achieve optimal cutting action.
Representative patents are U.S. Pat. No. 2,498,251 to Ernest S. Creel, U.S. Pat. No. 2,783,973 to Earl M. Weaver, U.S. Pat. No. 2,978,049 to Skidmore et al, U.S. Pat. No. 3,339,648 to Roscoe J. Blanton, U.S. Pat. No. 4,289,210 to William H. Schoeffler, U.S. Pat. No. 4,499,958 to Robert P. Radtke, Wilford V. Morris, U.S. Pat. No. 4,838,366 to A. Raymond Jones, U.S. Pat. No. 5,361,859 to Gordon A. Tibbitts, U.S. Pat. No. 5,560,440 to Gordon A. Tibbitts, U.S. Pat. No. 6,454,024 to Alan L. Nackerud.